The use of luminance and colour difference signals to represent pixel colour information is well known. This colour representation evolved to enable backward compatibility with monochrome television sets (which process the luminance signals) and in order to provide a degree of data compression.
Using one of the accepted terminologies, the luminance data is represented as Y and the colour difference signals are represented as U and V. It has been recognised that the colour data does not need to evolve as quickly as the luminance data for a given image quality to be perceived by the viewer. This provides scope for a reduction in data volumes, and different YUV schemes have evolved. Normal VHS video uses YUV 4:1:1 data, in which four times as much Y (luminance) data is provided as U or V data. The higher quality 4:2:2 YUV data format is used in the SVHS (Super-VHS) format and in other graphics applications. In the 4:2:2 format, two times as much Y data is provided as U or V data.
The luminance data is typically an unsigned value, namely a positive value in a given range. The colour difference information is derived from the subtraction of the red (for the U data) and blue (for the V data) colour component from the luminance value, and is a signed value. Processing of the different components of the YUV data therefore must take account of the different data types (signed and unsigned).